JRKH:
I wonder why these questions are always about “shooting” the abortion doctor…
It is somewhat stereotypical, for sure.
But the point is that if one is in situation to defend himself, or one’s family, or one’s neighbor, or one’s “extended” neighbor then it is morally allowed to use whatever force is necessary to prevent that, even using lethal force if necessary. Naturally, if a lesser “force” is sufficient, or one can dissuade the attacker without resorting to force at all, then one is obligated to use as little force as possible - to achieve the same result.
Also in real life it did happen (unfortunately) that some people
DID shoot the doctor, or stalked their family. As such the presented scenario is not too esoteric.
Now, if someone
actually believes that abortion
is murder, and knows that it is going to happen, then according to the accepted morals (which coincides with the church’s teaching) it is allowed to use as much force as necessary - and if the only recourse is to kill the doctor, that that is what must be done. However, there is a difference. In the usual scenario one is at the point of defending oneself (or the others) and one must act then and there. There is no other recourse, no calling for help. In the abortion example, there is the ability to go to the police, and say that Dr. X is an abortionist, and then demand that the police should step in and prevent the “murder”. The result would be — interesting

. The person probably would be told that abortion is not murder, just like a legally sanctioned execution is not murder, and probably would be sent home with a stern warning not to act as a vigilante. Or maybe the person would be considered deranged and put in a looney bin.
And if, after all that the person would still grab a gun and kill Dr. X, then he would be prosecuted and hopefully convicted on charge of first degree murder.
Of course, all that is legal stuff, not to be confused with the
perceived moral obligation of stepping in and preventing an attempted murder. If the perceived moral obligation is considered higher than the “law of the land” (and that is what the church teaches), then the person is obliged to go ahead and kill that doctor. Fortunately most people do not actually do that.